The present invention relates to combustion systems and particularly to an improved system for use in combusting a solid or liquid specimen to a gaseous sample for subsequent analysis.
In existing analyzers such as Model No. IR-33 sulphur determinator, commercially available from Leco Corporation of St. Joseph, Mich., the sulphur content of coal, coke, or other substances can be determined from a solid or liquid specimen which is positioned in an induction furnace and combusted to provide a gaseous sample. The gaseous sample is subsequently analyzed by an infrared detector detecting the sulphur dioxide concentration which is then displayed by a digital display as the sulphur content of the specimen. Certain aspects of the combustion system used in such prior art is disclosed in U.S. Pat. No. 3,923,464, issued Dec. 2, 1975, to Sitek, et al, and assigned to the present assignee.
Such systems are open ended and employ a carrier gas introduced into the combustion chamber of the induction furnace to oxidize the specimen and carry the resultant specimen gases through the opposite end of the combustion chamber and through an infrared cell for detection. A closed loop combustion system of this general type is described in U.S. Pat. No. 3,985,505, issued Oct. 12, 1976, to R. L. Bredeweg, and assigned to the present assignee.
Although these systems provide excellent results in analyzing a specimen, coal cannot be heated directly with radio frequency energy used in these devices since it is a nonconductor. As a result, accelerating agents such as iron chips or powder or tungsten are required to be added to the sample. Further, the combustion chamber in such systems is relatively small and due to the fact that the coal is naturally combustible and creates an exothermic reaction during its combustion, it tends to sputter and some of the specimen can easily escape from the hot zone of the combustion chamber and not be broken down to provide an accurate analysis.
U.S. patent application Ser. No. 958,967 filed on Nov. 9, 1978, entitled Combustion System discloses an improved closed end combustion chamber having a relatively large hot zone and an open end for receiving a combustion boat containing the specimen to be analyzed and an enclosed opposite end. The specimen gas is withdrawn from near the closed end of the combustion chamber by an eduction tube extending within the combustion chamber and the open end of the combustion chamber is effectively sealed by a gas curtain such that the interior of the chamber is available to the operator for readily inserting and removing specimens for combustion.
Although the enclosed combustion tube provides a significant improvement over the prior art it was discovered that on occasion, the floating end of the tube would fuse to its support block and differential movement in the order of 0.001 to 0.030 inches between the eduction tube and the combustion tube due to longitudinal expansion or contraction with temperature changes, warpage, and aging caused the eduction tube to fracture due in part to its relatively small size and therefore its fragility. Inasmuch as the eduction tube is anchored at one end to the combustion chamber and the free end could become fused to the spacing block employed in connection with the combustion system, such differential movement could not always be accommodated causing fracture of the eduction tube.
Also, it was discovered that with some highly volatile specimens, undesired ash, or other combustion by-products would, due to their vigorous combustion, fly from the combustion boat and tend to clog the eduction tube.